Transformer

ABSTRACT

A transformer wherein one of the windings provided on the legs of a transformer core to which is imparted a centripetal compression force resulting from the winding-axial component of a leakage flux is effectively supported by said core legs substantially at Octo- to dodeca-sectional points in the circumferential direction of said winding, thereby increasing the buckling strength of said winding as the latter is buckled by a compression force which is generated therein due to short circuit trouble occurring in a system with which said transformer is connected.

United States Patent Takashi Kuriyama;

Kiyoto Hiraishi; Tadashi Kiuchi; Sho Kusumoto; Shigeru Shida, Hitachi-shi, Japan Feb. 14, 1969 Mar. 2, 1971 Hitachi, Ltd.

Tokyo, Japan Feb. 16, 1968 Japan Inventors Appl. No. Filed Patented Assignee Priority TRANSFORMER 5 Claims, 4 Drawing Figs.

U.S. Cl 336/60,

Int. Cl. ..H0lf 27/08, HOlf 27/30 336/197, 210, 185,60

Field of Search [56] References Cited UNITED STATES PATENTS 1,317,280 9/1919 Ellis et a1, 336/197X 2,527,236 10/1950 Whitman 336/185X 2,756,397 7/1956 Cederstrom et a1. 336/185X 2,898,564 8/1959 Terry, Jr 336/197 3,447,112 5/1969 Brorermen et al 336/197X FOREIGN PATENTS 1,043,564 9/1966 Great Britain 336/210 1,094,442 12/1967 Great Britain 336/210 Primary ExaminerTh0mas J. Kozma Attorney-Craig, Antonelli, Stewart and Hill ABSTRACT: A transformer wherein one of the windings provided on the legs of a transformer core to which is imparted a centripetal compression force resulting from the winding-axial component of a leakage flux is effectively supported by said core legs substantially at octoto dodeca-sectional points in the circumferential direction of said winding, thereby increasing the buckling strength of said winding as the latter is buckled by a compression force which is generated therein due to short circuit trouble occurring in a system with which said transformer is connected.

TRANSFORMER I BACKGROUND OF THE INVENTION In general, said compression force is small in a steady state but when an excessive current is caused to flow through the winding as in the case where short circuit occurs in a system with which the transformer is connected, a much greater compression force is imparted to the winding, sothat finally the latter tends to be buckled thereby.

In the prior art, the reinforcing measure to prevent the winding from being buckled has been based on a view that such buckling can be prevented merely by increasing the number of support points at the inside of the winding.

In fact, by supporting the winding at the inside thereof with respect to the core with the aid of spacers of highrigidity, it is possible to make the buckling strength of the winding close to the limit value.

However, restriction is put on completely covering the inside of the winding with spacers, from the standpoint of the cooling for the winding and core. Thus, it has been a practice to provide a limited number of support points at the inside of the winding.

Let it be assumed that points for reliably supporting the inside of the winding with respect to the core are defined as effective support points, and that points merely inserted between the core and the insulating cylinder or between the insulating cylinder and the winding to determine the relationship in position therebetween are defined as general support points. In other words, in order to obtain effective support points, the spaces on the same radial lines of the cylinder winding between the inner periphery of the inner winding and the insulating cylinder and between insulating cylinder and the core may be filled with spacers having a high rigidity or large pressure receiving area so as to leave no gap in these portions which provide the support. Even in case there are no support points at the inside, the winding has initial buckling strength resulting from its own rigidity.

Referring to FIG. 4 wherein the buckling strength is indicated on the vertical axis and the number of support points on the horizontal axis, description will be made of the process in which the buckling strength of the winding changes from the initial buckling strength q, resulting from its own rigidity to the limit value of buckling strength q,.

As a result of the experiments performed by the inventors, it has been found that by increasing the number of the general support points, the buckling strength of the winding is increased only proportionally along a gentle line as indicated at A in FIG. 4 so that it is by no means possible to make it close to the limiting value of buckling strength q because the aforementioned cooling space should be provided.

The results of the experiments performed by the inventors with respect to various models show that by applying an inward or centripetal compression force to the winding, the latter is buckled when the resulting distortion becomes about 0.4 percent.

Thus, it is desired that the effective support points be capable of maintaining the aforementioned distortion within 0.2 to 0.3 percent when the above-described compression force is imparted thereto.

SUMMARY OF THE INVENTION As a result of the experiments performed by the inventors, it has been found that in the case where the support points at the inside of the winding are made to serve as effective support points and located at equisectional points on the circumference of the winding, the buckling strength of the winding is rapidly increased in the neighborhood of eight points so that it comes close to the limit value in the neighborhood of 16 points.

It has also been confirmed that such tendency remains unchanged even if some of the general support points are located between the effective support points.

The aforementioned effective support points can be provided by determining the pressure receiving area or. rigidity of the spacers so that the distortion is restricted within 0.2 to 0.3 percent when a centripetal compression force is imparted to the winding.

The present invention is characterized in that, in accordance with the foregoing experimental results, support points where a winding to which is imparted a centripetal compression force resulting from leakage flux produced by the winding and a current flowing therethrough is supported substantially with respect to the core legs are located substantially at Octoto dodeca-sectional points in the circumferential direction of the winding.

It is an object of the present invention to provide a transformer comprising a winding arrangement which is provided with increased strength for a radial compression force produced therein so as to be effectively protected from buckling.

Another object of the present invention is to provide a transformer comprising a winding arrangement which is so designed as to be effectively protected from buckling without reducing the cooling space for the winding and core.

In accordance with the present invention, distortion of effective support points located at equisectional positions can be made smaller than that of the winding which is caused by a compression force imparted thereto when a mechanical force is produced in the winding due to short circuit of the latter, so that the winding can be sufficiently reinforced with respect to buckling so that the buckling strength thereof can be increased substantially to the limit value.

Furthermore, in accordance with the present invention, the winding arrangement can be strengthened with respect to buckling without reducing the cooling space for the inside of the winding and the surface of the core.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial longitudinal sectional view showing a bifilar winding-type transformer;

FIG. 2 is a cross-sectional view showing about one-fourth of the transformer according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view showing about one-fourth of the transformer according to a second embodiment of the present invention; and

FIG. 4 is a view showing characteristic curves indicating the relationship between the number of support points at the inside of the winding and the buckling strength of the winding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 to 3, numeral 1 represents a transformer core comprising a leg portion la and a yoke 1 b, 2 an insulating cylinder fitted on the leg portion 1 b of the core I, 3 linear duct pieces arranged at a suitable interval in the circumferential direction of the inner surface of the insulating cylinder, and 4 a low voltage winding wound on the insulating cylinder 2 through the linear duct pieces. Further, numeral 5 denotes intercoil duct pieces arranged at a predetermined interval between the respective coils constituting the low voltage winding, 6 a clamp ring provided on the upper portion of the low voltage winding, and 7 an insulating ring provided on the clamp ring.

Numeral 8 indicates an insulation layer provided externally of the low voltage winding consisting of an alternate arrangement of insulating cylinders 8 a and oil gaps 8 b.

Numeral 9 shows a high voltage winding wound on the insulation layer 8 through a plurality of linear duct pieces arranged at a suitable interval externally of the insulation layer 8.

Numeral 11. represents intercoil duct pieces arranged between the respective coils constituting the high voltage transformer 9, 12 a clamp ring provided on the upper portion of the high voltage winding, and 13 an insulating ring provided on the clamp ring 12.

Each of the aforementioned insulating rings 7 and 13 is supported on the yoke 1 b of the transformer core 1 by means of a common insulating ring 14. Numeral 15 represents spacers interposed between the core leg portion 1 a and the insulating cylinder 2 at positions corresponding to octosectional points in the circumferential direction of .the low voltage winding 4. These spacers 15 are provided at the opposite end surfaces in the direction of lamination of silicon steel sheets constituting the core I, opposite end surfaces in the direction at right angles with respect to the direction of lamination and intermediate portions perpendicular to the respective end surfaces where the latter are adjacent to each other. Thus, in this case, the number of spacers 15 is eight. Numeral l6 denotes reinforcing spacers interposed between the low voltage winding 4 and the insulating cylinder 2 in opposing relationship to the back of the respective spacers l5, and 17 spacers serving as general support points which are suitably inserted in' the spaces between the insulating cylinder 2 and the core leg portion la to thereby support the insulating cylinder 2 circularly with respect to the core leg portion 1a.

The aforementioned spacers l and reinforcing spacers 16 constitute effective supporting points to provide increased strength for the low voltage winding 4, insulating cylinder 2 and core leg portion la, thus maintaining within 0.2 to 0.3 percent the distortion of these elements which is caused by an expected compression force imparted thereto.

The above-described effective support points may be effectively formed of wood having insulating oil impregnated thereinto, strongly compressed pressboard or the like.

Usually, the spacers l7 constituting the general support points are made of wood, and the linear duct pieces 3 provided on the surface of the insulating cylinder 2 are made of pressboard.

In the case where the Youngs modulus of the material of which are formed the spacers l5 and reinforcing support points is substantially equal to that of the material of which are formed the spacers 17 or linear duct pieces 3 constituting the general support points it is only required that the pressure receiving areaof the spacers constituting the effective support points be made greater than those of the spacers and duct pieces constituting the general support points.

In the embodiment shown in FIG. 2, the effective support points according to the present invention are established when the width of the silicon steel sheets forming the leg portion la of the core 1 is reduced so that the number of steps of the laminate is reduced.

Inthis embodiment, the spacers may be provided in the fanlike spacers defined between the steps of the laminate and theinsulating cylinder 2 in close contact therewith.

In the embodiment shown in FIG. 3, the effective support points according to the present invention are established when the number of varying width of the silicon steel sheets forming the leg portion la of the core 1 is increased so that the number of the steps of the laminate is increased.

In this case, the spacers l5 constituting the effective support points between the steps of the silicon steel sheet laminate may be formed in a zigzag shape corresponding to the shape of the stepped laminate. The means for constituting the effective support points can be established by making the aforementioned pressure receiving area greater than that of the general support points as described above, and it can also be established by making the rigidity of the spacers at the effective support points larger than that of the spacers at the general support points.

The number of effective support points according to the present invention may be increased, that is, it may be l2, 16 or greater, for example. As will be seen also from the characteristic curves B in FIG. 4, the buckling strength approaches the limit value in the neighborhood of 12 points to 16 points. Thus, by excessively increasing the number of support points, it is impossible to produce effect corresponding to the increase. Rather, it is undesirable to increase the number of effective support points, because of the fact that a cooling space should be established for the surface of the core leg portion la.

Practically, therefore, the optimum number of effective support points is 8 to 12.

Of course, a similar effect can be produced also by establishing the aforementioned effective support points within a range of i10 in the circumferential direction of the winding from the circumferential direction of the winding from the circumferential octododeca-sectional points of the winding.

We claim:

1. A transformer comprising a core having a leg portion anda yoke formed by laminating a multiplicity of silicon steel sheets, an insulating cylinder fitted on the core leg portion through a plurality of spacers arranged at optional intervals, a

plurality of linear duct pieces arranged on the surface of said insulating cylinder at optional intervals, and windings wound on said linear duct pieces, wherein spacers having higher rigidity than that of said spacers are internally and externally provided at octoto dodeca-sectional points on the circumference of said insulating cylinder.

2. A large capacity transformer comprising a core having a leg portion and a yoke formed by laminating a large number of steel sheets, a plurality of circular windings concentrically wound on the leg portion of said core with an insulating cylinder interposed therebetween, and general support points constituted by spacers disposed between said core and said insulating cylinder and disposed between said insulating cylinder and said windings in the axial direction of said windings, characterized in' that one of said windings'which is subject to a centripetal compressive force, caused by leakage flux produced by said windings and a current flowing through the conductors of said windings, is supported on said core leg through said interposed insulating cylinder with no gaps left therein, said support points being positioned on radial lines extending through octoto dodeca-sectional points on the inner periphery of said windings so that effective support points are obtained to thereby increase the buckling strength of said windings.

3. A transformer according to Claim 2, characterized in that said spacers which are disposed at the octoto dodeca-sectional points on the inner periphery of said windings, which are subject to the centripetal compressive force, are provided with pressure receiving areas contacting said core leg portion, said insulating cylinder and said windings, which are greater than those of the spacers of said general support points, to thereby provide said effective support points.

4. A transformer according to Claim 2, characterized in that the rigidity of the spacers disposed on the radial lines extending through octoto dodeca-sectional points on the inner periphery of said windings, which are subject to the centripetal compressive force, and between said windings and said insulating cylinder and between said insulating cylinder and said core leg portion, is greater than the rigidity of the spacers of the general support points, to thereby provide effective support points.

no gaps left therebetween, through said interposed insulating cylinder provided with spacers on the inner and outer peripheries thereof and on the radial lines extending through octoto dodeca-sectional points on the inner periphery of said inner windings, to thereby constitute effective support points, and further characterized in that said spacers are stronger than those of the general support points, to thereby reinforce the buckling strength of the inner winding. 

1. A transformer comprising a core having a leg portion and a yoke formed by laminating a multiplicity of silicon steel sheets, an insulating cylinder fitted on the core leg portion through a plurality of spacers arranged at optional intervals, a plurality of linear duct pieces arranged on the surface of said insulating cylinder at optional intervals, and windings wound on said linear duct pieces, wherein spacers having higher rigidity than that of said spacers are internally and externally provided at octo- to dodeca-sectional points on the circumference of said insulating cylinder.
 2. A large capacity transformer comprising a core having a leg portion and a yoke formed by laminating a large number of steel sheets, a plurality of circular windings concentrically wound on the leg portion of said core with an insulating cylinder interposed therebetween, and general support points constituted by spacers disposed between said core and said insulating cylinder and disposed between said insulating cylinder and said windings in the axial direction of said windings, characterized in that one of said windings which is subject to a centripetal compressive force, caused by leakage flux produced by said windings and a current flowing through the conductors of said windings, is supported on said core leg through said interposed insulating cylinder with no gaps left therein, said support points being positioned on radial lines extending through octo-to dodeca-sectional points on the inner periphery of said windings so that effective support points are obtained to thereby increase the buckling strength of said windings.
 3. A transformer according to Claim 2, characterized in that said spacers which are disposed at the octo- to dodeca-sectional points on the inner periphery of said windings, which are subject to the centripetal compressive force, are provided with pressure receiving areas contacting said core leg portion, said insulating cylinder and said windings, which are greater than those of the spacers of said general support points, to thereby provide said effective support points.
 4. A transformer according to Claim 2, characterized in that the rigidity of the spacers disposed on the radial lines extending through octo- to dodeca-sectional points on the inner periphery of said windings, which are subject to the centripetal compressive force, and between said windings and said insulating cylinder and between said insulating cylinder and said core leg portion, is greater than the rigidity of the spacers of the general support points, to thereby provide effective support points.
 5. A transformer comprising a core having a leg portion and a yoke, formed by laminating a large number of steel sheets, a pair of winding concentrically wound on said core leg portion with an insulating cylinder interposed therebetween, and a general support points constituted by spacers disposed between said core and said insulating cylinder and disposed between said insulating cylinder and the inner one of said windings in the axial direction of said windings, characterized in that said inner winding is supported on said leg core, with no gaps left therebetween, through said interposed insulating cylinder provided with spacers on the inner and outer peripheries thereof and on the radial lines extending through octo- to dodeca-sectional points on the inner periphery of said inner windings, to thereby constitute effective support points, and further characterized in that said spacers are stronger than those of the general support points, to thereby reinforce the buckling strength of the inner winding. 